require("expose?libraryName!./file.js");
// Exposes the exports for file.js to the global context on property "libraryName".
// In web browsers, window.libraryName is then available.

This line works to expose React to the web browser to enable the Chrome React devtools:

require("expose?React!react");

Thus, window.React is then available to the Chrome React devtools extension.

Alternately, you can set this in your config file:

  loaders: [
    { test: require.resolve("react"), loader: "expose?React" }
  ]

The require.resolve is a node.js call (unrelated to require.resolve in webpack processing -- check the node.js docs instead). require.resolve gives you the absolute path to the module ("/.../app/node_modules/react/react.js"). So the expose only applies to the react module. And it's only exposed when used in the bundle.

Documentation: Using loaders

MIT (http://www.opensource.org/licenses/mit-license.php)